The present invention is intended to improve on known apparatus used to mount a disc or discs on the spindle hub of a disc drive motor. Conventionally, the motor is located within the spindle hub of the disc drive, and one or more discs coated with magnetic material are attached to the spindle hub.
To facilitate mounting the disc or discs and supporting them in an aligned arrangement about the hub, a flange protrudes from the bottom of the cylindrical hub and the first disc or bottommost discs rest upon that flange. In a multiple disc arrangement alternating spacer rings and discs are stacked upon the first disc. A clamp ring is then attached to the opposite end or top of the cylindrical hub to apply pressure to the disc and spacer ring stack, thereby firmly holding the discs in a fixed position against the cylindrical hub.
In operation of the disc drive, the motor rotatably drives the hub and the disc or discs mounted thereon, allowing the information stored on circumferential tracks on the disc to be accessed by an associated read/write head. Each of these heads floats a small distance above the disc surface to sense the small magnetic signals stored on the tracks on the discs. Firm positioning of the discs is critical to reliable disc drive operation. The magnitude and location of the force imparted by the mounting hub and clamping ring is of critical importance to maintaining the position of the discs. Without proper clamping force, evenly and constantly applied, the discs, especially the first disc abutting the lower flange, will tend to move perpendicular to the direction of rotational motion, causing off-track error. Alternatively, an uneven application of forces, may impart a waviness to the disc. Because of the extremely small gap between the disc and the head flying above the disc in present technology, any waviness in the surface of the disc could cause the head to impact against the disc, causing permanent damage to the surface of the disc or the head.
It has been known to use disc mounting flanges that have been machined to have a flat mounting surface. This provided a large surface area for the disc to rest upon, but did not position the clamping force in an optimal location. In this situation, the clamping forces maximized very close to the cylindrical hub. This form of force distribution tends to bow the spacer disc and spacer stack, causing the discs no longer parallel to each other. Further, this machining of the hub flange is a relatively expensive proposition to implement. A further effort to solve the problem was the adoption of a knife edge or somewhat curved mounting surface at the periphery of the flange upon which the disc rests. However, this arrangement still causes the yielding of the material, which would prevent rework, or even breakage of a glass disc under shock because of the concentration of forces against a very limited portion of the disc. An example of this approach is shown in U.S. Pat. No. 5,089,922.
Thus, the known technology has not provided a solution to the problem of ensuring that a disc sitting against the flange of the hub will stay flat, assuming that the disc was flat to begin with.